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EUROPE
Mont Cleveland Sn Mine
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Mt. Cleveland Tin Mine, Luina, West Coast, Tasmania
Photo Rob Lavinsky |
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Mount Cleveland Mine, Luina, Tasmania
(Source-avec autoristation de Steve Sorrell, sur crocoite.com)
Minerals of the Mount Cleveland Mine, Luina, Tasmania Peter J. Hall Published in Volume 5, Number 3, of the Australian Mineralogist July-September, 1990
Abstract The Mt. Cleveland ore deposit is located near the township of Luina, 14km south west of Waratah (lat. 41o28' S, long. 145o24' E) in north west Tasmania. The Aberfoyle Resources Ltd. Mt. Cleveland mine had a life span of 19 years and is well known to collectors for producing a quantity of well-crystallized, aesthetic mineral specimens, in particular fluorite, calcite and quartz. Although the mine has been closed for four years, a more thorough examination of specimens previously collected has also brought to light a number of well-crystallized rare species.
History
The Mt. Cleveland deposit was originally discovered in 1898 by prospectors panning the Whyte River and its tributaries for gold. The deposit was found as gossan outcrops on the eastern foothills of Mt. Cleveland. At the time of the discovery they were believed to be the cappings of silver-lead lodes. It was not until 1900, when the site was visited by Harcourt Smith, the Government Geologist, that the gossan was analysed and the presence of tin was detected.
The first lease on the deposit was taken out by Mr. Sydney Coundon of Waratah and shortly after the Cleveland Tin Mining Co. N.L. was formed. The Company began operations in 1908 with a capital of 7,500 Pounds in 65,000 shares (M. Godfrey, 1984).
The gossanous ore was mined from a series of open cuts and the company erected a 10-head stamp battery and concentrating plant on-site to treat the ore. The gossan proved to be very shallow and quickly gave way to sulphide mineralisation. With the plant and technology available at the time, the recovery of tin proved extremely difficult, with an estimated 45 per cent of the tin content being lost in the crushing and concentrating process. This low recovery rate made the original Cleveland mining operation uneconomic, and the company ceased operations in 1914. However the mine and mill were let on tribute for the next three years, until a sharp fall in the price of tin in 1917 forced the tributors out of business.
Mines Department records show that during these early operations about 345 tons of tin concentrates were recovered from 40,000 tons of ore, worth about 34,000 Pounds (M. Godfrey, 1984).
In the following years there was occasional prospecting on this site.
In 1935 the Mt. Bischoff Mining Co. excavated two short adit crosscuts and drove for short distances on portions of the Halls and Battery Lodes and obtained large bulk ore samples, apparently intended for removal to Waratah for testing. Despite spending 5,000 Pounds over two years on this exercise, the ore samples were carefully "paddocked" but never removed.
During 1953 and 1954 the Tasmanian Department of Mines, in conjunction with the Bureau of Mineral Resources, conducted a series of geological and geophysical surveys of the Cleveland area embracing the known lode outcrops. As a result they were able to define a number of large, coincident self potential and magnetic anomolies.
In 1961, Aberfoyle Tin Development Partnership initiated a sequence of exploratory programmes consisting of test drilling and underground development for geological mapping and sampling. By 1965 the exploratory programme had proven an ore reserve of more than 3 million tons averaging 0.91% tin and 0.38% copper (K. Pink, 1984).
In September 1966 the Cleveland Tin N.L. company was formed to operate the new mine. After a construction period of 18 months the company officially commenced production on January 14, 1968. Mining continued until May 1986 when the last of the payable ore had been extracted. During the mine's operating life it became the second largest producer of tin concentrate in Australia, behind Renison.
Geology
The Mt. Cleveland orebodies are part of the Hall Formation which is believed to have been deposited as finely bedded calcarous mud or pelitic limestone during the Middle-Upper Cambrian. Burial and diagenesis were followed by a period of intense structural deformation and gentle warping during the Upper Devonian Tabberabberan Orogeny. This resulted in the host rock forming a series of sub-vertical lenses. A period of acid igneous activity followed, a late stage of which was marked by the permeation of the country rocks by mineralising fluids associated with cooling granite magma. Metasomatic replacement of the host rock by these "ore fluids" led to the mineralisation of the lode bed (Cox and Glasson, 1971).
The Mt. Cleveland mineralised zone contains four major replacement-type lodes - Hall's, Henry's, Luck's and Khaki lodes. Hall's is the main lode and consists of a series of 4 lenses between 3 and 15m wide (Ransom and Hunt, 1975).
The orebodies have a NE-SW strike, and dip between 90 o-75 o, with a 40 o southerly pitch. They extend up to 600 metres in length and approximately 350 metres in depth.
In addition to the replacement bodies, two other minor styles of mineralisation were recognised - a greisenized granite porphyry dyke and vein stockworks (Jackson, 1985).
Mineralogy
During the first mining period at Cleveland, very little detail was recorded on the mineral present. It was not until the latest period of mining - 1968-1986 - by Aberfoyle that detailed analyses were carried out and the deposit's mineralogy was revealed.
The chief ore minerals are cassiterite, chalcopyrite and stannite; these rarely formed good crystals. In contrast, the main gangue minerals, quartz, dolomite, siderite, calcite, 'tourmaline', fluorite and chlorite were found in abundance in well crystallized forms.
Miners probably commenced collecting the more aesthetic minerals soon after mining commenced in 1968.
Actinolite
The minor occurrence of actinolite was reported by Ransom and Hunt (1975) and Jackson (1985). It occurred as scattered small crystals which are part of a complex combination of minerals which form part of the sulphide host rock or the mineralized lenses, generally in the upper replacement bodies.
Albite
Albite is recorded by Jackson (1985) as a minor rock-forming mineral in veins and the greisen.
Ankerite
As recorded by Jackson (1985), ankerite commonly occurs as fine-grained material which is optically indistinguishable from dolomite or calcite.
"Apatite"
Jackson (1985) has listed "apatite" as occurring in minor to trace amounts. The specific member of the apatite group was not given.
Arsenopyrite Arsenopyrite is one of the more common accessory sulphides at Cleveland. It occurs mainly as euhedral grains throughout the ore bodies and occasionally in cavities as well-formed lustrous metallic crystals up to 30mm long. Single crystals are rarely observed, the most predominant form being 'cockscomb' crystal aggregates. The arsenopyrite crystals are usually found in association with crystals of siderite and fluorite.
Axinite Axinite as recorded by Jackson (1985) has only been found in trace amounts at Cleveland. No reference was made as to which member of the axinite group was detected. Bertrandite Bertrandite is rather rare and was only recently detected on a few specimens. It mainly occurred as colourless bladed crystals to 3mm with small orthoclase (var. adularia) crystals. However, on one specime it occurred as translucent pale blue/gray bladed crystals, forming fan-shaped aggregates up to 6mm across on a siderite and fluorite matrix.
Biotite Biotite is abundant at Cleveland in the replacement bodies (Jackson, 1985), with three varieties recognised. Reddish-brown biotite is found in association with fluorite in the lower replacement bodies; khaki biotite occurs at intermediate levels with green biotite above. Biotite also occurs as fine to coarse aggregates in early vein stages. Each of the biotite varieties is high in iron and low in magnesium.
Bismuth Native bismuth is a common accessory mineral in the early-formed veins at Cleveland (Jackson, 1985), where it often shows partial alteration to bismuthinite. In the other styles of mineralization at Cleveland, bismuth only occurs in minor amounts. Bismuthinite Bismuthinite is a minor mineral in all styles of mineralization (Jackson, 1985) but was locally abundant in some veins.
Calcite Calcite is quite common at Cleveland and occurs in a variety of crystallized habits, from scalenohedral to simple rhombohedral crystals. The scalenohedral crystals are up to 30mm long whereas the the rhombohedral crystals rarely exceed 8mm across. Most crystals are colourless to to white and as one of the last minerals to form, calcite is often found encrusting other minerals, usually quartz.
Cassiterite Cassiterite at Cleveland mainly occurs as subhedral-euhedral grains 0.02-0.07mm across, occurring singularly or in aggregates, distinctly concentrated in the quartz/dolomite-rich laminae. On rare occasions it has been found in cavities as isolated single crystals up to 6mm across usually associated with crystals of quartz and fluorite.
Chalcocite Chalcocite from Cleveland has been recorded by Cox and Glasson (1971) as a minor mineral throughout the ore-body, forming microscopic grains or alteration rims around other sulphides. Chalcopyrite Chalcopyrite mainly occurs as anhedral grains 0.02-0.25mm across which are typically intimately intergrown with pyrrhotite, sphalerite and stannite. It has only rarely been sighted as crystals up to 3mm across in cavities associated with siderite.
Chlorite Chlorite is very common throughout the ore-bodies as green/grey radiating crystals up to 0.5mm across. It is generally one of the last minerals to form, so it occurs as coatings on most of the crystallized minerals in cavities. It is also thought to replace aggregates of carbonate and sulphide. It also must have formed earlier in the sequence as it has been found as inclusions in quartz crystals.
Cordierite Cordierite was recorded by Mason (1970) as forming due to magnesian solutions from the country rock reacting with quartz from the ore-body in areas subjected to high temperatures. Covellite Covellite was recorded by Cox and Glasson (1971) as one of the minerals occurring in minor amounts throughout the ore-body, mainly as microscopic grains or alteration rims around primary sulphides.
Danalite Danalite is present only in minor amounts in the replacement bodies at Cleveland (Jackson, 1985). The danalite is crimson and similar to garnet in appearance and occurs as crystals up to 15mm across.
Dolomite Dolomite is very common throughout the ore-bodies. It occurs as small subhedral plates up to 0.5mm across and as irregular aggregates up to 0.3mm across intergrown with and replacing quartz (Ransom and Hunt, 1975). In cavities it occurs as pearly white, saddle-shaped crystals up to 10mm across and is most commonly found with siderite encrusting crystals of quartz and fluorite.
Fluorite
Fluorite is a dominant mineral in the replacement bodies and veins. It may comprise up to 50% of the rock in some zones in the replacement bodies and up to 80% of vein-filling material in late stage veins (Jackson, 1985). Massive material was mainly colourless to deep purple in colour. Specimens showing well developed crystals were the most spectacular and most sought-after by the miners. The best specimens recovered consisted of colourless to pale blue/green cubic crystals up to 12cm across. Many specimens were associated with colourless quartz crystals, minor drusy dolomite and siderite.
Galena Galena is not common at Cleveland but it has been sighted as crystals up to 3mm across in both the cubic and the octahedral forms. It is usually associated with quartz, siderite and chlorite.
Gearksutite Gearksutite has been identified from Cleveland on only a few specimens, where it occurs as sugary aggregates of white crystals to 1mm encrusting quartz crystals. It is associated with crystals of a ralstonite-like mineral, morinite and vivianite (Birch and Pring, pers. comm. 1990).
Graphite Graphite is present in trace amounts in the greisen and wallrock alterations enveloping veins (Jackson, 1985).
Grunerite Grunerite occurs in the lower replacement bodies at Cleveland and appears to form secondarily after ferroan hastingsite in the presence of a fluorine-enriched fluid (Jackson, 1985).
Gypsum Gypsum as 'rose gypsum' crystals was recorded by Miller (1974), in a list of minerals being collected by miners. No other details were given. Hastingsite Ferroan hastingsite is the dominant amphibole at Cleveland, where it is found extensively in the central part of the replacement bodies (Jackson, 1985). It occurs as acicular bluish green masses up to 2cm across, often associated with tourmaline.
Hematite Hematite was noted by Ransom and Hunt (1975) as a minor accessory mineral. Ilmenite Ilmenite as recorded by Jackson (1985) is a minor phase in all styles of mineralization at Cleveland.
Magnetite Magnetite is restricted to certain areas within the replacement ore-bodies, where it is thought to represent relict primary skarn (Jackson, 1985). Crystals are usually small, euhedral and in aggregates. Marcasite Marcasite is relatively common at Cleveland. Throughout the ore-body it occurs as replacement margins around pyrite and pyrrhotite grains, frequently almost completely replacing these earlier sulphides. It is also relatively common as radiating crystals forming iridescent spheres up to 8mm across, usually coating fluorite or siderite.
Molybdenite Molybdenite is not very common and occurs as masses of platy crystals up to 6mm across associated with wolframite and bismuth enclosed in quartz.
Monazite Monazite at Cleveland was recorded by Jackson (1985) in trace amounts in association with apatite in late-stage veins. Morinite Morinite is one of the rarer minerals at Cleveland. It has only been found on a few specimens as greyish to colourless blocky crystals up to 2mm across. It occurs with 'adularia' and ralstonite encrusting crystals of quartz and fluorite (Birch and Pring, pers. comm. 1990).
Muscovite Muscovite occurs in two forms. The main form is as massive fine-grained "sericite", which is finely disseminated throughout the lower sections of the ore-bodies (Ransom and Hunt, 1975). Muscovite has also been observed as fawn/grey spherical aggregates of crystals about 1mm across usually as coatings or masses with and on quartz crystals in the cavities.
Orthoclase The orthoclase from Cleveland has proven to be the variety known as 'adularia' (Birch and Pring, pers. comm. 1990). It forms as brilliant white, blocky crystals up to 6mm long and has been found in association with fluorite, bertrandite and the F-bearing minerals.
Pyrite Throughout the ore-body pyrite occurs as euhedral cubic grains ranging in size from 0.05 to 2mm, commonly enclosed by, and sometimes partly replaced by other sulphides. It also commonly occurs as cubic crystals in cavities, usually forming drusy coatings on fluorite, siderite and calcite. Striated cubes up to 5cm across have occasionally been found in solution veins (Jackson, 1985).
Pyrrhotite Pyrrhotite is the dominant sulphide in the ore-body where it occurs mainly as anhedral masses from 0.1mm to several cm across. In this form it is most commonly intimately intergrown with chalcopyrite, sphalerite and stannite. To a lesser extent, it occurs as thin hexagonal platy crystals up to 5mm across, usually associated with sphalerite and quartz.
Quartz Quartz is locally common and widespread throughout the ore-bodies. It was one of the first minerals to form in the cavities, and as a result is usually found at least partly coated by other minerals. Crystals of quartz are up to 30cm long and usually colourless to white, with the larger crystals often containing inclusions. In certain zones of the ore-bodies, Japanese twin crystals are common but these rarely exceed 15mm. A small number of smoky quartz crystals were also recovered; most were stubby, doubly terminated and up to 50mm long. The smoky colouring is not uniform in these crystals, but forms distinct random zones.
Ralstonite A ralstonite-like mineral is one of the rarer and more recently identified minerals from Cleveland. Analyses of these ralstonites has shown that a substantial amount of calcium has substituted for sodium, and therefore it is best described as calcian ralstonite. It occurs as colourless to white octahedral crystals up to 2mm across, either as individuals or as clusters. The "ralstonite" has formed on quartz crystals in association with morinite, gearksutite, vivianite and fluorite (Birch and Pring, pers. comm. 1990).
Rhodochrosite Rhodochrosite is only a very minor mineral, as spherical aggregates of pink crystals up to 10mm across, in association with crystals of quartz and calcite. Rutile Rutile is found as a minor phase in all styles of mineralization at Cleveland (Jackson, 1985).
Scheelite Scheelite has a restricted occurrence in the lower replacement bodies and appears to represent relict primary skarn. Scheelite is also found as rims on some wolframite crystals in veins (Jackson, 1985).
Sellaite Sellaite, the magnesium analogue of fluorite, is a minor but wide-spread mineral at Cleveland. Sellaite is most abundant in the late-stage fluorite/topaz-rich veins (Jackson, 1985).
Siderite Siderite is the dominant carbonate and occurs in the replacement bodies, veins and greisen. Although the majority of the siderite is massive, crystals do occur and are best developed in the veins and vughs. It mainly forms as small rounded rhombohedral crystals forming drusy coatings but it also has been found as attractive bladed fan-shaped crystals up to 30mm in diameter.
Sphalerite The sphalerite from Cleveland has an iron content of approximately 14% which means it is the variety known as martite (Cox and Glasson, 1971). The sphalerite generally occurs as anhedral masses 0.1 to 2cm across and is usually intimately intergrown with pyrrhotite and chalcopyrite. Crystallized sphalerite is rare but it has been found as isolated crystals up to 10mm across associated with siderite.
Stannite Stannite was recorded by Cox and Glasson (1971) as distinct rims up to 0.2mm thick on cassiterite and some of the earlier formed sulphides, particularly pyrrhotite, chalcopyrite and sphalerite.
Talc As recorded by Jackson (1985), talc only occurs in trace amounts in the veins. Tetrahedrite Tetrahedrite was recorded by Cox and Glasson (1971) as a minor accessory sulphide occurring throughout the ore-bodies.
Topaz At Cleveland topaz is abundant in the greisen and in veins. Quartz-topaz greisen contains up to 50% modal topaz, whereas topaz is the dominant vein-filling material in late-stage veins. In veins, coarse topaz crystals (up to 4cm across) have grown perpendicular to the vein walls, and contain abundant fluid inclusions (Jackson, 1985).
Tourmaline The exact species of the tourmaline group occurring at Cleveland has not been determined. Throughout the ore-body the tourmaline occurs as strongly pleochroic (colourless-light green) anhedral to euhedral grains 0.05 to 1mm in length. Where it is prominent in the ore-body it shows a preferred orientation parallel to the original bedding (Cox and Glasson, 1971). In cavities it occurs as dark green to black needle-like crystals forming fan-shaped aggregates up to 20mm across and is usually associated with siderite, dolomite or calcite. Vermiculite An iron-rich vermiculite was recorded by Jackson (1985).
Vivianite Vivianite crystals are one of the more attractive mineral occurrences. It occurs as transparent green/blue columnar crystals up to 10cm long and 6mm across, usually striated parallel to the 'c' axis. Due to the fragile nature of the crystals, most are found detached from the matrix. Very few crystals on matrix were recovered and terminated crystals are rare. The matrix specimens are associated with crystals of quartz, "ralstonite", gearksutite and siderite.
Wolframite As recorded by Cox and Glasson (1971), wolframite occurs as small euhedral prismatic crystals which are commonly orientated parallel to the original bedding in the chlorite-rich laminae. Wolframite is also abundant in the early forming veins along with quartz, molybdenite and fluorite. Wollastonite In sections of the lodes subject to temperatures over 500 o C, quartz and dolomite have reacted to form wollastonite (Mason, 1970).
References
Cox, R. and Glasson, K.R. (1971) Economic Geology of the Cleveland Mine, Tasmania, Economic Geology, Vol. 66, pp. 861-878.
Godfrey, M. (1984) Waratah, Pioneer of the West.
Jackson, P. (1985) Minerals of the Tin Mines, pp. 64-80. Minerals of Tasmania. Combined Mineralogical Societies Seminar.
Mason, A.C.C. (1970) Tin Ore Deposits of Mt. Cleveland, Eighth Commonwealth Mining and Metallurgical Congress, Vol. 1, Geology of Australian Ore Deposits, pp. 503-505.
Miller, B. (1974/5) Minerals from the Mountain Mines, Australian Gems and Crafts Magazine, Dec./Jan.
Pink, K. (1984) The Tasmanian West Coast Story.
Ransom, D.M. and Hunt, F.L. (1975) Cleveland Tin Mine, Economic Geology of Australia and Papua New Guinea, No. 1, Metals, pp. 584-591.
An update to the minerals of the Mount Cleveland Mine is currently underway and will be published here soon.
